1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to an image drum for a printing apparatus, and more particularly, to an image drum which can improve productivity and reduce a manufacturing cost by simplifying a connecting method between ring electrodes formed on a circumferential surface of a drum body and a control board mounted with a control chip individually applying a voltage to the ring electrodes, and a method of manufacturing the image drum.
2. Description of Related Art
FIG. 1 is a perspective view illustrating a related art image-forming element according to a related art, and FIG. 2 is a partially enlarged cross-sectional view illustrating a portion of the circumferential wall of the image-forming element according to the related art. The image-forming element shown in FIGS. 1 and 2 is disclosed in U.S. Pat. No. 6,014,157 by reference.
Referring to FIGS. 1 and 2, a related art image-forming element 10 includes a hollow cylindrical drum body 12 which is made of metal, such as aluminum or an aluminum alloy. A plurality of circumferentially extending electrodes 14 are formed on the outer circumferential surface of the drum body 12. These electrodes 14 are electrically insulated from one another and from the drum body 12 and are covered by a thin layer of insulating material. The electrodes 14 may generally be designed in various manners depending on the desired resolution of the images to be formed, but are preferably, but not necessarily, provided densely over the whole length of the drum body 12 and arranged with a pitch of, for example, about 40 μm in order to realize a resolution of approximately 600 dpi.
An elongate-shaped control unit 16 is mounted inside of the hollow drum body 12 such that a terminal array 18 formed at a longitudinal side face of the control unit 16 adjoins the internal wall of the drum body 12. The control unit 16 is arranged for individually applying a suitably high voltage to each of the electrodes 14 via the terminal array 18 in accordance with the desired image formation. As shown in FIG. 2, the individual electrodes 14 are formed as grooves separated by adjacent insulating ridges 20 and are filled internally with electrically conductive material 32. Since the electrically conductive material 32 fills in a small diameter hole 24 and a large diameter hole 26 constituting a through-hole 22, the electrodes 14 are electrically connected to zebra-strips 36 disposed at the inner wall surface of the drum body 12 via the through-hole 22. In this case, an anodized surface layer 34 is present at the outer circumferential surface of the drum body 12 and at the internal wall of the through-holes so as to electrically insulate the drum body 12 and the electrodes 14 from each other.
In order to manufacture the image-forming element 10, the cylindrical drum body 12 is provided. The grooves are cut into the outer circumferential surface of the drum body 12, for example by means of a diamond chisel to have a pitch of approximately 40 μm and a width of approximately 20 μm to form the electrodes 14. Alternatively, these grooves may be formed on the outer circumferential surface of the drum body 12 by means of a laser beam or an electron beam.
In the next step, the large diameter holes 26 are cut into the wall of the drum body 12 from inside by, for example, a means for a laser beam. The small diameter holes 24 may also be formed with a laser beam, either from the inside or outside of the drum body 12 to thereby form the through-holes 22. After the through-holes 22 including the small diameter holes 24 and the large diameter holes 26 have been formed, the whole drum body 12 is anodized so as to form the insulating metal oxide layer 34 on the whole surface of the drum body 12. Thereafter, the electrically conductive material 32 fills in the grooves and the through-holes 22. The outer or inner circumferential surface of the drum body 12 is cut to a predetermined depth through polishing so as to effectuate the electrodes 14 and electrical connection portions inside of the through-holes 22. An insulating layer is formed on the outer circumferential surface of the drum body 12 and the control unit 16 is disposed inside of the drum body 12 so as to complete the manufacture of the image-forming element 10.
As described above, in order to form the electrodes 14 on the outer circumferential surface of the drum body 12, the grooves are densely formed over the whole length of the drum body 12 using a precise cutting tool and the through-holes 22 must be formed at regular intervals either from the inside or outside of the drum body 12. Also, after the formation of the anodized surface layer on the outer circumferential surface of the drum body 12 and at the internal wall of the through-holes 22, the electrically conductive material 32 is filled into the grooves and the through-holes 22 and then removed until a desired thickness remains. It is particularly difficult to make a pattern of a line in the metal of the surface of the drum body 12 since the surface of the drum body is curved.
In general, it is difficult to form a mold of a photoresist by photolithography on a curved surface. Also, a gravure printing method may be considered, but a resolution of 600 dpi (dots per inch) may not be possible because ring electrodes with a pitch of about 40 μm may not be able to be realized.
Also, a technology, such as a nano-printing technology or an nano imprinting technology, may make a small sized pattern less than 10 ηm. However, the technology is generally applied to a flat surface and an additional etching process is needed.